Method for forming a composite container with high barrier liner layer

ABSTRACT

A composite container includes a high barrier inner liner member including a metal layer of vacuum-deposited aluminum parallel with and spaced from the longitudinal edge of a synthetic plastic base thereby to define a first web that is helically wound in edge-overlapping relation such that one longitudinal edge of the metal strip overlaps the other longitudinal edge of the metal strip by a given distance (d). The overlapping edges of the first web are hermetically joined by a heat-sealable bond between an adhesive layer covering the metal strip and the adjacent face of the first web, and a compatible heat-sealable layer on the opposite face of the web. According to the method for forming the container, the first web is formed by longitudinally slitting a supply web having longitudinally extending spaced metal strips on one face thereof along lines of severance spaced from the edges of the metal strips, so that the edges of the metal strip in the helically wound liner layer will be isolated from the container contents. The resultant container provides high storage stability, particularly for contents that are corrosive to aluminum.

BACKGROUND OF THE INVENTION

The present invention relates to a composite container including atleast one tubular fibrous body wall, and a high barrier inner linermember covering the inner surface of said body wall, which compositecontainer is adapted for holding liquids, corrosive products, andproducts which require storage at non-atmospheric conditions. A highbarrier liner is necessary if the composite container in which the linermember is used is to hold a pressured product, such as carbonatedliquid, a vacuumed product, such as nuts or potato chips, or productsflushed with an inert gas. It is desirable that the liner contain atleast one layer of aluminum since aluminum is one of the mostcost-effective means for achieving oxygen and water vapor resistance.

The various liner constructions presently employed in compositecontainers adapted for holding liquids, corrosive materials andnon-atmospheric pressurized products possess certain serious drawbacks.For example, in the prior "Anaconda fold" construction--as taught by theKrause U.S. Pat. No. 3,156,401--an edge folding technique for helicallywound layers is disclosed which possesses the drawback that is producesa comparatively thick step in the body wall thickness. Even with tough,thin liner components, the step is relatively thick since it containsthree layers of liner. Secondly, if a stress is imposed across the linerheat seal, such as by the body resisting internal pressure, the seal ispulled in a peel mode. A heat seal stressed in peel has a stressconcentration along the edge of the seal and is far weaker than if theseal were stressed in shear. Thirdly, owing to the round shape of therolled edge of the fold, there is too often a channel under the sealwhich cannot be properly sealed off by the end compound in the seamwhere the liner heat seal meets the metal end.

In the "free foil" liner disclosed in the Wannamaker et al U.S. Pat. No.3,428,239 and Ahlemeyer U.S. Pat. No. 3,520,463, for example, apaperless film-foil laminate is heat sealed to form an overlapped seam.A problem with this construction for a container which is to hold liquidbeverages is that the contained product is free to attack the bare foiledge. Even if the product is not spoiled by the dissolved metal, theseam will be weakened and will open, whereby the can will leak.

In the lapped liner heat seal type of seam construction shown in theKrause U.S. Pat. No. 3,288,341, a tape member is provided over thelapped liner heat seal. While the taped lap seal is thinner than theAnaconda fold, the extra thickness of the tape makes more difficult thetask of achieving a hermetic seal with the ends. Applying the tapeduring the tube winding operation and keeping it properly alignedadversely affect line efficiency. Furthermore, the additional expense ofthe additional tape member is a cost factor to be avoided.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acomposite container including at least one tubular, fibrous body walllayer and a high barrier inner liner layer, which container is adaptedfor holding liquids, corrosive materials, gas flushed, and pressured orvacuumed products. More particularly, it is a primary object of thepresent invention to provide a composite container which includes aliner member having a metal layer no part of which is exposed to theinterior of the composite container in which the liner is used.

A further object of the present invention is to provide a compositecontainer including a metallized liner member which affords an improvedleakproof rolled seam connection with the metal end closure member.

An additional object of the present invention is to provide a compositecontainer including a liner member which is helically wound inedge-overlapping heat sealed relation wherein the lapped edges aresealed in a strong, durable and leakfree manner.

The composite container according to the present invention includes atleast one tubular, fibrous body wall and a high barrier inner linermember. The inner liner includes a synthetic plastic film and a thinmetal layer, on the order of 1×10⁻⁶ inch thick, of metallized materialdeposited on at least one face of the base film at intervalscorresponding to the width of the individual rolls of liner, thereby todefine metal-free strips parallel to the edge of the web. The innerliner member further includes a first layer of heat sealable syntheticplastic material covering the other face of the metallized film, and asecond layer of heat sealable synthetic plastic material covering themetallized surface of the base film. The innermost heat sealable surfaceand the exposed sealable surface over the metallized layer are selectedto be heat seal compatible with each other.

According to a further object, a method for forming composite containersis provided, wherein the inner liner is helically wound inedge-overlapping heat sealed relation to form a tube. The individualrolls of liner are slit so the edge-overlapping on the interior of thecontainer includes one of the metal free strips. The overlappingdistance of the edges of the inner liner is sufficient to cause theadjacent edges of the metallized band to be in overlapping relation,whereby the metallized region extends completely around the interior ofthe container body wall to provide product protection, the edges of themetallized band being isolated from the container contents.

As a consequence of the invention, a high barrier liner construction isprovided including a straight lapped joint, which high barrier liner isresistant to most food products, including aqueous and greasy foods. Theliner assures a hermetic sealed connection with the metal end closuremembers, and the liner is particularly suited for use in connection witha rolled end and heat sealed membrane end closure. The liner produces amuch smoother interior of the container, facilitating dispensing by aplunger. As for example, in containers for caulking material, grease andthe like. The high barrier liner will have an absolutely minimum effectupon the flavor or odor of the container contents.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will becomeapparent from the following detailed description when viewed in thelight of the accompanying drawing, in which:

FIGS. 1-4 are cross-sectional views of various liner memberconstructions of the prior art, respectively;

FIG. 5 is a partial cross-sectional view of a composite containeraccording to the present invention;

FIG. 6 is a top view of the web member of the present invention;

FIG. 7 is a cross-sectional view of the web member taken along line 7--7of FIG. 6;

FIG. 8 is a cross-sectional view of the lapped heat seal of the presentinvention showing the relative position of the metallized layer on eachedge of the seal taken along line 8--8 of FIG. 10;

FIG. 9 is a diagrammatic illustration of the manner for calculating therequired width of the metallized band between the metal free strips;

FIG. 10 is a top view of the helical winding process employed to formthe composite container of the present invention;

FIGS. 11 and 12 are detailed sectional views of the lap joints of twoalternate embodiments of the invention, respectively;

FIGS. 13-16 illustrate examples of laminates suitable for use with thepresent invention; and

FIG. 17 is a table comparing the physical properties of various specificexamples of the invention.

DETAILED DESCRIPTION

Referring first more particularly to FIG. 1, the prior art type of innerliner heat seal most often produced for composite containers is known asan "Anaconda fold", as disclosed by U.S. Pat. No. 3,156,401. The linerincludes a backing layer 10, a metal foil layer 12, and a heat sealablefilm layer 14, which liner layer is arranged on the inner surface offibrous body wall 16 having an outer label layer 18. For carbonatedbeverage containers, the Anaconda fold construction has the inherentdrawbacks referred to above. For example, owing to the round shape ofthe rolled edge of the fold, an undesirable channel is formed under theseal which cannot be properly sealed off by the end compound in the seam21 where the liner heat seal meets the metal end.

FIG. 2 illustrates a prior art paperless film-foil laminate heat sealedfront to back to form an overlapped joint. Such a liner construction issometimes known as a "free foil" liner. Film layer 20 is laminated withmetal foil layer 22 and the overlapping edges of the laminate are bondedby sealing layer 24. The liner is located adjacent fibrous body wall 26.A problem with this construction for liquid beverages is that thecontained product is free to attack the bare foil edge 28. Even if theproduct is not spoiled by the dissolved metal, the seam will be weakenedand will open whereupon the can will leak.

FIG. 3 discloses the prior art construction including a tape member 38lcoated over the lapped liner heat seal. The film and metal foil layers30 and 32, respectively, are laminated together and helically wound, theoverlapping edges being bonded by sealant 34. If done properly, the tape38 isolates the product from the metal foil edge 35. The liner islocated adjacent the inner surface of fibrous body wall 36. The tape isadhered to the liner surface with a pressure sensitive adhesive.

FIG. 4 discloses a proposed type of lapped liner heat seal forprotecting the edge of the foil, which has proven to be commerciallyimpractical to manufacture in a large scale production process, since itis not commercially feasible to remove (by skiving, for example) thefoil from the edge at location 46 of the film (40) foil (42) laminate.Moreover, it is difficult to clearly remove a strip of 0.00035 in. foilfrom a 0.001 in. thick film by a machine that is to run continuously. Aheat seal coating is still required to make the lap seal. Another methodto produce a laminate whose foil layer does not extend to the edge wouldbe to design the laminator to use foil narrower than the film. Thiswould require the use of film only as wide as one roll of liner (i.e., 6inches) or at the most, two widths wide. Running multiple narrow widthsof foil with wider film is not believed to be possible with anyequipment in existence. Furthermore, owing to the thickness of the foilrelative to the film, the absence of the foil from location 46 to theedge of the roll would cause the edge to be very soft and easilydamaged. Another option for achieving the configuration of FIG. 4 is tolaminate narrow foil to film in-line on the tube winder. However,adhesive application and drying problems, the need for quick tack, andalignment problems prevent serious contemplation of in-line laminatingof free foil.

Referring now to the construction of the present invention illustratedin FIG. 5, the composite container includes a metal end closure member52, and a composite body member 54, including an outer label layer 56(for example, a paper/foil laminate), at least one fibrous body walllayer 58, and an inner liner layer 60. An end sealing compound 61 isprovided between composite wall and the metal end, as is conventional inthe art.

With reference to FIGS. 6 and 7, the inner liner layer 60 is formed froma supply web 70 which includes a synthetic plastic film 72 having alayer of metallized material 74, preferably of aluminum, deposited byvacuum deposition on at least one face of said base layer web 72. Themetallized layer 74 is applied with the aid of masks so that it containsmultiple parallel sharply defined metal-free strips 65. The metal-freestrips have a predetermined width (a), and are parallel with and spaceda predetermined distance (b) from one another and from the edges of webmember 70, the predetermined distances (a) and (b) being important tothe invention, as will be set forth in greater detail below. The sum ofthe distances (a) and (b) constitute the width of an individual roll ofliner when slit along lines 84. The slitting line 84 is positioned adistance (c) from one edge of a metal-free strip. The value of (c) istypically 0.05 in. It must exceed the tolerance of the equipment used toslit the individual rolls, to prevent exposure of metal on the edge. Theoutermost two metal layers 74 are spaced from the longitudinal edges ofthe web by the edge portions 72a of synthetic plastic layer 72.

FIG. 8 shows a detailed sectional view taken through the lapped heatseal of the present invention normal to the longitudinal edge of theweb. Adjacent edges of the metallized layer 74 overlap each other by adistance (d). Distances (a) plus (d) equal the total width of the heatsealed lap.

In theory, distance (d) may be quite small. It need be only sufficientlylarge that the lateral permeability across distance (d), of gases fromor toward the product, is small compared to the permeability through themetallized layers. In practice, distance (d) must be sufficiently greatso that dimensional tolerances in metallizing, slitting or winding thetube, do not produce a failure to overlap the metallized edges (anegative value of (d)). Experience has shown that with good productionpractices, an allowance of 0.1 in. for the distance (d) is sufficient.

The thickness of the step at the lap is the thickness of one layer ofthe finished liner. In the preferred embodiments, this dimension is lessthan 0.002 in. and may be as low as 0.001 in. On the other hand, withthe commonly practiced prior art of FIG. 1, the thickness of the step istwice the liner thickness. Paper-backed liners employed are commonly0.025 to 0.045 in. thick, for a single ply. Thus, with the presentinvention, the step at the liner joint is 1/9 to 2/7 as thick ascommonly practiced. Thus substantial reduction in the thickness of thelap greatly facilitates achieving a hermetic connection with the metalend closure members.

Referring to FIG. 9, the width of the metallized band (b) is dependentupon the angle (α) the axis of the liner makes with the axis of thewinding mandrel 90. The angle (α) is measured from a line drawn normalto the axis of the mandrel. It is the acute angle the liner makes withthe cut end of a tube. Hereafter (α) is known as the winding angle. Thevalue of (b) is also dependent upon the diameter of the winding Dmandrel (90) which establishes the inner circumference of the tube. Asshown in FIG. 9:

    (b-d)/πD=sin α

whereupon:

    b=(πD sin α)+d

It should be noted that the winding angle of the liner will be slightlylarger than the winding angle of an outer ply label whose printingmatches perfectly. Specifically, Tan α Label/Tan α Liner=D/(D+2W) whereW is the total thickness of the body wall of the tube.

Successive layers of the liner web 60, fibrous paperboard layer 58 andlabel layer 56 are wound on the mandrel as shown in FIG. 10, the lineredge heating means 92 being illustrated diagrammatically.

Referring again to FIG. 7, the metallized layer 74--preferably,aluminum--is applied, for example by vacuum deposition, upon a base film72. While the metallized coating is relatively thin, (approximately1×10⁻⁶ inches) it very substantially improves the barrier properties ofthe base film. The amount of metal applied per unit area is important tothe present invention in that the amount must be sufficient to provide abarrier to oxygen, water vapor and carbon dioxide. The amount of metalapplied is most conveniently inferred from measuring the optical densityof the metallized film. For this invention, individual metallized layershave an optical density no less than 2.6 and no more than 3.5. Themetallized layer being negligible in thickness compared to the basefilm, there is no appreciable variation in thickness of the linermaterial between the metallized bands and the metal-free spacestherebetween. Preferably, the base film is selected from the family offilms classified as oriented polyethylene terephthalate. The base filmincludes a discrete sealing layer 76, for example, a coextrudedcopolyester. To the metallized surface is applied a second resinouslayer 71 (for example, oriented polyethylene terephthalate) with anexposed surface layer 78 (for example, a coextruded polyester). Thesecond resinous layer is attached to the metallized surface by anadhesive layer 80 (for example, of polyurethane). Alternately, thesecond resinous layer may be an extrusion coating, in which case, thelayer 80 in a primer and the exposed surface 78 cannot be distinguishedfrom layer 71.

In all instances, it is a characterizing feature of the presentinvention that surface 76 must heat seal securely to surface 78.Whichever surface is exposed to the product must be compatible with, andresistant to, the product. Furthermore, the bond between surfaces 76 and78 must not separate when the composite body is flanged in preparationfor attaching a metal end. This invention benefits from the fact thatthe heat seal is stressed in the shearing mode. As such, it is muchstronger than if the geometry caused the bond to be stressed in thepeeling mode, as is the case with the Anaconda fold.

The second resinous layer 71 may, in fact, be indentical to the basefilm, which of course, makes surfaces 76 and 78 the same andautomatically heat seal compatible. Thus, as shown in FIG. 11, thesecond film 171 is also strip metallized, in which case the metal-freestrips 174a and 174b are laminated in registry. As will be seen in TableI, exceptional barrier results from this construction. Alternately, asshown in FIG. 12, the base film 272 may be strip metallized on bothsides with layers 274a and 274b, and sandwiched between two heatsealable films 276 and 278 (for example, heat sealable orientedpolypropylene), as shown in FIG. 12.

A further requirement for the product contact surface, 76 or 78, is thatit must have sufficient mobility over a winding mandrel to allow tubesto be wound. The opposite exposed surface must allow it to be adhered tothe inner ply of paperboard by any of the known techniques. Betweensurfaces 76 and 78, they must have sufficient thickness and flow toallow a hermetic seal to be made. Neither surface should have beenapplied from a solvent solution, i.e., heat seal lacquer. Such lacquerstypically contain low molecular weight polymers which are susceptible tosoftening by product components. The product contact surface must notadd to or subtract from the flavor of the product. The linerconstruction must meet FDA requirements.

Specific examples of constructions which meet the various criteria setforth above, are as follows, reference being made to Table I of FIG. 17.

EXAMPLE NO. 1

Referring to FIG. 11, a 48 gage (i.e., 0.00048 inch) Melinex 850 (ICIAmericas, Inc.) film 172 (formed of an oriented polyester coextrudedwith a copolyester sealing layer) is strip metallized on itsnon-sealable surface by the vacuum deposition of aluminum with a maskand is bonded by a layer of high performance adhesive (such as apolyurethane/polyester adhesive) to a corresponding layer 171 with themetallized strips 174a and 174b being in registry. Alternatively, themetal strips 174b on the second Melinex 850 sheet may be omitted. CamvacInternational, Inc. of Brewster, N.Y. has demonstrated its ability tometalize polyester film leaving sharply defined metal-free spaces.

EXAMPLE NO. 2

Same as above except Melinex is 60 ga. and the increase in gage is duetotally to an increase in thickness of the sealing layer. Film isdesignated as Melinex 3093.

EXAMPLE NO. 3 (FIG. 13)

48 ga. Melinex 850 strip 372 provided with metallized strips 374 onnon-sealable surface and laminated with high performance adhesive 380 tothe uncoated side of a 1 mil high density polyethylene (HDPE) filmcoated with polyvinylidene chloride (PVDC) layer 378. A suitable PVDCcoated film is available from Arnold Cellophane of Miami, Fla.Copolyester sealing surface 376 is towards the product. A suitableadhesive is Morton Chemical Co's. Adcote 548. The copolyester sealinglayer of the Melinet film seals tightly to the PVDC layer of the secondfilm, the HDPE layer assisting in producing a hermetic seal.

EXAMPLE NO. 4

Referring to FIG. 14, a 50 ga. M-24 Mylar sheet (E.I. DuPont DeNemours &Co., Inc.) 472 having a PVDC layer 476 is provided on its uncoated sidewith metallized strip 474, and is laminated by layer 480 of highperformance adhesive (such as urethane/polyester adhesive to a 1.5 milcoextruded polyolefin film (DSF 300, Crown Advanced Films, San Leandro,Calif.) having layers 482, 484 and 486 of propylene, polyethylene andethylene vinyl acetate (EVA) respectively, the EVA surface beingexposed.

In the modification of FIG. 15, the laminating adhesive layer 480' bondsthe M-24 Mylar sheet to a 1 mil layer of high density polyethylene 486that is coated with an exposed layer 488 of PVDC. The PVDC surface ofthe Mylar seals firmly and hermetically to the EVA surface.

EXAMPLE NO. 5

Referring to FIG. 16, a 50 gage M-24 Mylar sheet 572 is metallized onits uncoated side to define the aluminum strip 574, and is extrusioncoated over a catalyzed primer 580 with a layer 582 of 15 #/3000 ft. sq.18% (UE 652-00, U.S. Industrial Chemicals Co.) vinyl acetate copolymer.The PVDC surface 576 of the Mylar is exposed to the product. The PVDCsurface seals tightly and hermetically to the EVA coating.

What is claimed is:
 1. A method for forming a helically wound compositecontainer, comprising the steps of:(a) vacuum depositing on a first faceof a supply web (72) of synthetic plastic material a plurality ofparallel spaced first metal strips (74) arranged in parallel relation tothe longitudinal edge of said web, said supply web being coated on itsopposite face with a first layer (76) of heat-sealable material; (b)coating the metal strips and the adjacent exposed portions of said firstsupply web face with at least one second layer (78) of a heat-sealablematerial compatible with said first heat-sealable layer; (c)longitudinally severing said supply web along parallel lines ofseverance (84) each extending in spaced relation between the adjacentlongitudinal edges of a successive pair of said metal strips,respectively, thereby to define at least one first inner liner web (60),each line of severance being spaced a given distance (c) from thecorresponding edge of the associated metal strip, respectively; (d)helically winding the first web (60) on a mandrel in edge-overlappingrelation such that the longitudinal edge of one metal strip overlaps theother longitudinal edge of that strip by a given distance (d); and (e)heat sealing together the adjacent surfaces of the overlapping edgeportions of said first web, thereby to define a reinforcingliquid-impervious tubular inner liner structure.
 2. The method asdefined in claim 1, and further including the step of(f) helicallywinding at least one fibrous body wall layer (58) on the outer surfaceof said inner liner layer.
 3. The method as defined in claim 2, andfurther including the step of(g) helically winding at least one labellayer (56) on the outer surface of said fibrous body wall layer.
 4. Themethod as defined in claim 1, and further including the preliminary stepof bonding between said first face of said supply web (72) and saidsecond heat-sealable layer (78) a second web (71) of synthetic plasticmaterial.
 5. The method as defined in claim 4, wherein said second webis bonded to said supply web by a layer of adhesive (80, 180).
 6. Themethod as defined in claim 5, wherein said second web includes a metalstrip (174b) parallel and in registry with a corresponding metal stripon said supply web.
 7. The method as defined in claim 1, wherein saidsupply web (272) is provided on its said opposite face with a secondmetal strip (274a) parallel and in registry with a corresponding firstmetal strip (274b), said second metal strip and the adjacent exposedportion of said opposite face being coated by said first heat sealablelayer (276).